>> couric: good evening, everyone. the world watched stunned as terrorists trained in pakistan attacked mumbai, india, nearly two years ago. they killed more than 170 people and wounded 300. now officials say terrorists tied to al qaeda have been planning new attacks just like it in europe, and some of the recent c.i.a. drone attacks in pakistan may have been launched to disrupt the plot. justice correspondent bob orr is following this still-developing story. bob, the details of the european plot are absolutely chilling. >> reporter: well, katie, yes, they are. u.s. and european officials say the plot called for a spectacular multi-pronged attack on numerous cities in great britain, france, denmark, and germany. teams of terrorists, trained by an al qaeda-linked group along the pakistan-afghan border, plan to carry out commando-style shooting sprees. patterned on the mumbai attacks of 2008. sources describe the plot as credible, but say it was discovered at an early stage and had not gone operational. still, terror experts say there is much they don't know.